As part of "Ramp Jam," eight freeway on-and off-ramps along I-405 and ramps on Wilshire Boulevard will be closed in phases between two weeks or as long as 90 days. Construction begins on June 22 and will be an ongoing project throughout the length of the year.

The first 90-day closures are the two Wilshire Boulevard ramps:

For the westbound Wilshire Boulevard on-ramp to the 405 North, motorists were advised to travel northbound on Sepulveda Boulevard to access the Moraga Drive on-ramp or travel southbound on Sepulveda Boulevard to access the Santa Monica on-ramp.

For the 405 North off-ramp to westbound Wilshire, motorists were advised to exit the freeway using the Santa Monica Boulevard off-ramp, then travel northbound on Sepulveda Boulevard to Wilshire Boulevard. Motorists can also take the off-ramp at Sunset Boulevard.

Vehicles traveling northbound on the I-405/I-10 will be directed to exit at Bundy Drive to reach their original westbound Wilshire destinations.

The six other Wilshire ramps were expected to be closed consecutively, some two at a time. A closure schedule for the remaining ramps was expected to be announced at a later date.

Officials urged motorists not to use local residential streets to detour through the area.

These are already some of the biggest ramps in the country, and traffic and congestion will likely get worse before it gets better.

The I-405 Sepulveda Pass Improvements Project aims to add a 10-mile HOV lane on the northbound I-405 between the 10 and 101 freeways in the Valley.

According to the Metro website, crews will work around the clock to rebuild the new on-and off-ramps once the closures begin. Most of the ramps will have to be demolished and completely rebuilt, which includes new pillars and new supports. In addition, the concrete will have to set, which takes 28 days.

"Construction crews will be working day and night, 24/7 to get this work completed as quickly as possible. But the honest truth is, and we have to be transparently blunt about this, we're going to be here for a while with some of the worst traffic congestion we've seen in a long time," said Los Angeles County Supervisor Zev Yaroslavsky.

The Santa Monica on-ramps to both the southbound and northbound 405 will also be closed, but the closures slated to involve the largest number of commuters are the ones along Wilshire Boulevard.

In advance of the closures, city leaders and transportation officials are urging commuters to plan ahead, adjust travel times or carpool to minimize frustrations on the road. Officials said traffic officers will be directing traffic at key intersections along Wilshire, Santa Monica, Sunset and Sepulveda boulevards when construction gets under way.